240 ESSENTIALS OF BACTERIOLOGY 



fully in steam and not overheated, so as to prevent inversion 

 of the sugar. 

 Examination for Bacillus Coli and Sewage Bacteria. 



Instead of examining for typhoid bacilli, sewage contamina- 

 tion is best indicated by the presence of the colon group of 

 organisms, although their abundance rather than mere pres- 

 ence is to be considered. There are many closely related 

 bacteria which give reactions similar to the Bacillus coli, but 

 they are chiefly of fecal origin, and for practical purposes 

 they can be included in the colon group. 



General Characteristics of Colon Group. i. Fermentation of 

 dextrose and lactose with gas-production. 2. Short bacillus, 

 non-liquefying, Gram negative. 



The committee of the Public Health Association recom- 

 mends the following procedure: 



Two Methods. Method a. Applicable for sewage waters. 

 Preparation of an agar plate with a known volume of water, 

 using lactose litmus-agar and incubating at 40 C. Bacillus 

 coli will show its presence by red colonies (acid fermentation 

 of the sugar); further testing is then needed to fully identify. 

 Not all red colonies Bacillus coli. 



Method b. Cultivation, at 40 C., of a measured quantity 

 of water in a fermentation tube containing a sugar broth. 

 If gas appears, a portion of the liquid is plated as in method a. 



Additional Details. If in twenty-four hours no red colonies 

 appear in the agar-lactose litmus Petri dishes, Bacillus coli 

 is considered absent, providing the sample was a polluted 

 one, so that the bacilli, if present, would be in a concentrated 

 form. Only i or 2 c.c. of water can be used, because the 

 ordinary water-bacteria spread rapidly and contaminate the 

 other bacteria. 



// acid-forming colonies are found, five or six are fished for 

 subcultures on slanted agar, in fermentation tubes, milk, 

 gelatin, peptone solution, and nitrate broth. 



If the water is not strongly contaminated, an underground 

 water, for instance, or a mountain stream, the better way is 

 to inoculate two or three lactose or dextrose bouillon fermen- 



